Implement straightforward overload general metrics.

- OOM metric
- onionskin overload metric
- DNS timeout metric

src/core/or/relay.c

@@ -83,6 +83,7 @@
 #include "feature/nodelist/routerlist.h"
 #include "core/or/scheduler.h"
 #include "feature/hs/hs_metrics.h"
+#include "feature/stats/rephist.h"
 
 #include "core/or/cell_st.h"
 #include "core/or/cell_queue_st.h"
@@ -2720,6 +2721,9 @@ cell_queues_check_size(void)
   if (alloc >= get_options()->MaxMemInQueues_low_threshold) {
     last_time_under_memory_pressure = approx_time();
     if (alloc >= get_options()->MaxMemInQueues) {
+      /* Note this overload down */
+      rep_hist_note_overload(OVERLOAD_GENERAL);
+
       /* If we're spending over 20% of the memory limit on hidden service
        * descriptors, free them until we're down to 10%. Do the same for geoip
        * client cache. */

src/feature/relay/dns.c

@@ -63,6 +63,7 @@
 #include "feature/relay/dns.h"
 #include "feature/relay/router.h"
 #include "feature/relay/routermode.h"
+#include "feature/stats/rephist.h"
 #include "lib/crypt_ops/crypto_rand.h"
 #include "lib/evloop/compat_libevent.h"
 #include "lib/sandbox/sandbox.h"
@@ -1547,6 +1548,16 @@ evdns_callback(int result, char type, int count, int ttl, void *addresses,
 
   tor_addr_make_unspec(&addr);
 
+  /* Note down any DNS errors to the statistics module */
+  if (result == DNS_ERR_TIMEOUT) {
+    /* libevent timed out while resolving a name. However, because libevent
+     * handles retries and timeouts internally, this means that all attempts of
+     * libevent timed out. If we wanted to get more granular information about
+     * individual libevent attempts, we would have to implement our own DNS
+     * timeout/retry logic */
+    rep_hist_note_overload(OVERLOAD_GENERAL);
+  }
+
   /* Keep track of whether IPv6 is working */
   if (type == DNS_IPv6_AAAA) {
     if (result == DNS_ERR_TIMEOUT) {

src/feature/relay/onion_queue.c

@@ -33,6 +33,7 @@
 #include "core/or/circuitlist.h"
 #include "core/or/onion.h"
 #include "feature/nodelist/networkstatus.h"
+#include "feature/stats/rephist.h"
 
 #include "core/or/or_circuit_st.h"
 
@@ -163,15 +164,19 @@ onion_pending_add(or_circuit_t *circ, create_cell_t *onionskin)
 #define WARN_TOO_MANY_CIRC_CREATIONS_INTERVAL (60)
     static ratelim_t last_warned =
       RATELIM_INIT(WARN_TOO_MANY_CIRC_CREATIONS_INTERVAL);
-    char *m;
+    if (onionskin->handshake_type == ONION_HANDSHAKE_TYPE_NTOR) {
-    if (onionskin->handshake_type == ONION_HANDSHAKE_TYPE_NTOR &&
+      char *m;
-        (m = rate_limit_log(&last_warned, approx_time()))) {
+      /* Note this ntor onionskin drop as an overload */
-      log_warn(LD_GENERAL,
+      rep_hist_note_overload(OVERLOAD_GENERAL);
-               "Your computer is too slow to handle this many circuit "
+      if ((m = rate_limit_log(&last_warned, approx_time()))) {
-               "creation requests! Please consider using the "
+        log_warn(LD_GENERAL,
-               "MaxAdvertisedBandwidth config option or choosing a more "
+                 "Your computer is too slow to handle this many circuit "
-               "restricted exit policy.%s",m);
+                 "creation requests! Please consider using the "
-      tor_free(m);
+                 "MaxAdvertisedBandwidth config option or choosing a more "
+                 "restricted exit policy.%s",
+                 m);
+        tor_free(m);
+      }
     }
     tor_free(tmp);
     return -1;